Epoxy resin composition

ABSTRACT

Storage-stable, thermally-curable, one-part epoxy resin compositions comprising a curable epoxide resin; a curative amount of an aliphatic or non-aromatic cyclic polyol having about 2 to 18 carbon atoms, at least two hydroxy groups of said polyol being primary or secondary, and said polyol being free of strong acid groups, and free of electron-withdrawing substituents and large groups which cause steric hindrance in the α-position in relation to the carbon atoms attached to the methylol groups of the polyol; and a catalytic amount of an imidazole compound.

This is a continuation of application Ser. No. 205,330 filed June 10,1988, now abandoned, which is a division of application Ser. No. 132,709filed Dec. 11, 1987 now U.S. Pat. No. 4,772,645, issued Sept. 20, 1988which is a continuation of application Ser. No. 860,511 filed May 7,1986, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to latently curable one-part epoxy resincompositions.

Epoxy resins, i.e., organic compounds having one or more terminal orpendant oxirane groups, ##STR1## have been widely used for many years inadhesive compositions. Various curatives, accelerators, and additiveshave been used with the epoxy resins to modify the curing properties andadhesive characteristics.

U.S. Pat. No. 3,553,166 (Anderson et al.) and U.S. Pat. No. 3,677,978(Dowbenko et al.) disclose storage stable, elevated temperature curableepoxy resin compositions which contain epoxy resin and, as a curingagent, a metal salt complex of an imidazole. Anderson further disclosesthe addition of nitrogenous compounds to improve structural strength.

Other various curing systems disclosed for use with epoxy resins includedialky/amino-alkylimidazoles in U.S. Pat. No. 3,912,689 (Bechara et al.)fluoroalkylsulfonate salts of a metal coordinated with imidazole orsubstituted imidazole ligands in U.S. Pat. No. 4,101,514 (Thom),phthalic acid derivatives which are substituted by alkenylamino groupsin U.S. Pat. No. 4,140,703, imidyl-and isoimidyl-phthalic anhydrides inU.S. Pat. No. 4,160,081 (Kvita et al.), imidyl-benzene-dicarboxylic and-tricarboxylic acid derivatives in U.S. Pat. No. 4,233,220 (Kvita etal.), imidazole accelerators with aromatic polyol hardeners in U.S. Pat.No. 4,246,162 (Schreiber), isocyanate blocked imidazoles andimidazolines in U.S. Pat. No. 4,355,228 (Beitchman et al.), naphthyldiisocyanate blocked imidazole in U.S. Pat. No. 4,533,715 (Lee et al.),solutions or eutectic mixtures of imidazoles withN,N'-dihydroxyethyl-5-,5-dimethyl hydantoin or trimethylpentanediol inU.S. Pat. No. 4,417,010 (Shimp) and a liquid blend of an imidazole and amixture of trimethylolpropane and 1,4-butanediol in European PatentApplication No. 0 118,270 (Celanese).

SUMMARY OF THE INVENTION

The present invention provides storage-stable, thermally-curable,one-part epoxy resin compositions comprising a curable epoxide resin; acurative amount of aliphatic or non-aromatic cyclic polyol having about2 to 18 carbon atoms, at least two hydroxyl groups of said polyol beingfree of strong acid groups and primary or secondary, and said polyolbeing free of electron-withdrawing substituents, and large substituentswhich would cause steric hindrance, in the α-position in relation to thecarbon attached to the methylol group of the polyol and preferably beinginsoluble in the epoxide resin; and a catalytic amount of an imidazolecompound selected from

(a) compounds represented by the formula

    M.sup.1 (L.sup.1).sub.a (X.sup.1).sub.b

where

M¹ is Ni⁺⁺, Cu⁺⁺, or Co⁺⁺,

L¹ is ##STR2## where R² is alkyl having 1 to 18 carbon atoms, cyanoalkylhaving 1 to 4 carbon atoms, phenyl, or substituted phenyl, and R³ isalkyl having 1 to 18 carbon atoms, phenyl, or substituted phenyl,

X¹ is --R⁴ (COO⁻)₂ where R⁴ is phenyl, naphthyl, or C_(m) H_(m-1) wherem is 0, 1, or 2, or

X¹ is --R⁵ (COO⁻)_(e)

where

R⁵ is phenyl or naphthyl and

e is 3, 4, or 5, or

X¹ is an anion of a strong inorganic acid, i.e., an acid having a pK_(a)of less than 2,

a is 2, 4 or 6, and

b is 0.5, 0.67, 1, or 2 depending on the valence of X¹ ;

(b) compounds represented by the formula L² X²

where

L² is ##STR3## where R⁶ is --H, --C_(n) H_(2n+1) or ##STR4## n being anumber of from 1 to 16, R⁷ is --H, --CH₃, --C₂ H₅, --C₂ H₄ CN, or##STR5## R⁸ is --H, --CH₃, --C₂ H₅, --CH₂ OH, or ##STR6## R⁹ is --H or--CH₂ OH X² is --R⁴ (COOH)₂ where R⁴ is phenyl, naphthyl, or C_(m)H_(2m-1) where m is 0, 1, or 2, or

X² is --R⁵ (COOH)_(e)

where

R⁵ is phenyl or naphthyl and

e is 3, 4, or 5, or

X² is isocyanuric acid, and

(c) compounds represented by the formula

    M.sup.3 (L.sup.3).sub.e

where

M³ is Ni⁺⁺, Cu⁺⁺, Co⁺⁺, Zn⁺⁺, Cu⁺, or Ag⁺,

L³ is ##STR7## where R¹ is --H, ##STR8## or C_(n) H_(2n+1), n being anumber of from 1 to 16, and each R² is --CH₃, ##STR9## or --CH₂ OH, e is1 or 2;

(d) compounds represented by the formula

    L.sup.4

where L⁴ is ##STR10## where R⁶, R⁷, R⁸ and R⁹ are the same as forcompound (b); and

(e) a compound represented by the formula ##STR11## wherein X, Y, and Zmay be the same or different, and each may be hydrogen, a lower alkyl oraryl having 1-12 carbon atoms, halo or nitro.

The composition also preferably contains a toughening agent. A flowcontrol agent may also be present.

The composition is thermally curable by application of heat, e.g., inthe range of 100° to 200° C.

The cured composition is useful as an adhesive, and in coatings, andmolded, cast, and potted products. As an adhesive, the compositionprovides excellent shear and impact strength.

DETAILED DESCRIPTION OF THE INVENTION

Epoxide group-containing materials useful in the compositions of theinvention are glycidyl ether derivatives having an oxirane ringpolymerizable by ring opening. Such materials, broadly called glycidylether epoxides, include monomeric epoxy compounds and epoxides of thepolymeric type.

These epoxide group-containing materials can vary from low molecularweight monomeric materials to high molecular weight polymers and canvary in the nature of their backbone and substituent groups.Illustrative permissible substituent groups include halogens, ethers,and siloxane groups. The molecular weight of the epoxy-containingmaterials can vary from 50 to about 100,000 or more. Mixtures of variousepoxy-containing materials can also be used in the composition of thisinvention.

Such epoxide group-containing materials are well-known and include suchepoxides as glycidyl ether type epoxy resins and the diglycidyl ethersof bisphenol A and of novolak resins, such as described in "Handbook ofEpoxy Resins" by Lee and Neville, McGraw-Hill Book Co., New York (1967).

These epoxide group-containing materials which are useful in thepractice of this invention include glycidyl ether monomers of theformula ##STR12## where R¹ is alkyl or aryl and m is an integer of 1 to6. Examples are the glycidyl ethers of polyhydric phenols obtained byreacting a polyhydric phenol with an excess of chlorohydrin such asepichlorohydrin (e.g., the diglycidyl ether of bisphenol A, i.e.,2,2-bis (4,4'-epoxy propoxyphenyl)propane).

There are a host of commercially available epoxide group-containingmaterials which can be used in this invention. In particular, epoxideswhich are readily available include glycidol, diglycidyl ethers ofbisphenol A (e.g., those available under the trade designations Epon™828 available from Shell Chemical Co., and DER™-331, DER™-332, andDER™-334 available from Dow Chemical Co.), diglycidyl ethers ofbisphenol F (e.g., Epiclon™ 830 available from Dainippon Ink &Chemicals, Inc.) silicone resins containing diglycidyl epoxyfunctionality, flame retardant epoxy resins (e.g., DER™-580, abrominated bisphenol type epoxy resin available from Dow Chemical Co.),1,4-butanediol diglycidyl ethers (e.g., Araldite™ RD-2 available fromCiba-Geigy), polyglycidyl ethers of phenol formaldehyde novolak (e.g.,DEN™-431 and DEN™-438 available from Dow chemical Co.), and resorcinoldiglycidyl ethers (e.g., Kopoxite™ available from Koppers Company,Inc.). Preferably the epoxide group-containing material is thediglycidyl ether of bisphenol A or bisphenol F. Most preferably theepoxide group-containing material is the diglycidyl ether of bisphenolA.

The polyols useful in the present invention are aliphatic ornon-aromatic cyclic polyols having 2 to 18 carbon atoms, at least twohydroxyl groups, preferably at least three hydroxyl groups, with atleast one hydroxyl group, preferably at least two hydroxyl groups beingprimary. The polyol should be free of strong acids, and free ofelectron-withdrawing substituents such as --COOH, --CONH₂, ##STR13##--CH₂ X where X is halogen, and large groups which cause sterichindrance, in the α-position in relation to the carbon atom attached tothe methylol group of the polyol. Such groups, except strong acidgroups, can be present in positions other than α to the carbon attachedto the methylol group of the polyol. The term "polyol" also includesderivatives of the above-described polyols such as the reaction productof the polyol with di- or poly-isocyanate, or di- or poly-carboxylicacid, the molar ratio of polyol to --NCO, or --COOH being 1 to 1. Thepolyol is preferably insoluble in the epoxide resin to increase storagestability.

The polyol is present in the composition in a curative amount, i.e., anamount which is sufficient to react with the epoxide and cause thecomposition to cure more rapidly when heated. The addition of thecurative amount of the polyol provides the composition with areactivity, i.e., the length of time for exotherm to peak when held, at137° C., of less than about 10 minutes, more preferably less than about5 minutes, most preferably less than about 2 minutes. Preferably, thepolyol is present in an amount to provide a hydroxyl to epoxide, i.e.,##STR14## ratio of about 0.5:1 to 1:1, more preferably about 0.7:1 to0.8:1.

Examples of preferred polyols include trimethylyol ethane, trimethylolpropane, trimethyol aminomethane, ethylene glycol, 2-butene-1,4-diol,pentaerythritol, dipentaerythritol, and tripentaerythritol. Other usefulpolyols include 1,3-butane diol, 1,4-butane diol, 2-diethyl-1,3-pentanediol, and 2,2-oxydiethanol.

The imidazole compounds useful in the present invention are compoundsselected from

(a) compounds represented by the formula

    M.sup.1 (L.sup.1).sub.a (X.sup.1).sub.b

where

M¹ is Ni⁺⁺, Cu⁺⁺, or Co⁺⁺,

L¹ is ##STR15## where R² is alkyl having 1 to 18 carbon atoms,cyanoalkyl having 1 to 4 carbon atoms, phenyl or substituted phenyl,e.g., ethylphenyl, diphenyl or tolyl, R³ is alkylene having 1 to 18carbon atoms, phenyl, or substituted phenyl,

X¹ is --R⁴ (COO⁻)₂ where R⁴ is phenyl, naphthyl, or C_(m) H_(2m-1) wherem is 0,1, or 2, or

X¹ is --R⁵ (COO⁻)_(e)

where

R⁵ is phenyl or naphthyl and

e is 3,4, or 5, or

X¹ is an anion of a strong inorganic acid, i.e., an acid having a pK_(a)of less than 2,

a is 2, 4 or 6, and

b is 0.5, 0.67, 1, or 2 depending on the valence of X¹ ;

(b) compounds represented by the formula

    L.sup.2 X.sup.2

where

L² is ##STR16## where R⁶ is --H, C_(n) H_(2n+1) or ##STR17## n being anumber of from 1 to 16, R⁷ is --H, --CH₃, --C₂ H₅, --C₂ H₄ CN, ##STR18##R⁸ is --H, --CH₃, --C₂ H₅, --CH₂ OH, or ##STR19## R⁹ is --H or --CH₂ OHX² is --R⁴ (COOH)₂ where R⁴ is phenyl, naphthyl, or C_(m) H_(2m-1) wherem is 0, 1, or 2, or

X² is --R⁵ (COOH)e

where

R⁵ is phenyl, or naphthyl and

e is 3, 4, or 5, or

X² is isocyanuric acid, and

(c) compounds represented by the formula

    M.sup.3 (L.sup.3).sub.e

where

M³ is Ni⁺⁺, Cu⁺⁺, Co⁺⁺, Zn⁺⁺, Cu⁺, or Ag⁺,

L³ is ##STR20## where R¹ is --H, ##STR21## or C_(n) H_(2n+1), n being anumber of from 1 to 16, and each R² is --CH₃, ##STR22## or --CH₂ OH, eis 1 or 2; and

(d) compounds represented by the formula

    L.sup.4

where L is ##STR23## where R⁶, R⁷, R⁸ and R⁹ are the same as forcompound (b); and

(e) a compound represented by the formula ##STR24## wherein X, Y and Zmay be the same or different, and each may be hydrogen, a lower alkyl oraryl having 1-12 carbon atoms, halo or nitro.

The imidazoles or imidazole containing compounds, hereinafter termed"imidazoles" are present in the composition in catalytic amounts, i.e.,amounts sufficient to catalyze the reaction between the epoxide resinand the polyol on heating of the composition. Preferably, the amount ofthe imidazole used is about 1 to 10 weight percent, more preferablyabout 3 to 7 weight percent based on the weight of the epoxide andpolyol present. Preferably the imidazole is insoluble in the epoxideresin to provide increased storage stability.

Examples of suitable imidazoles include hexakis (imidazole) nickelphthalate, hexakis (imidazole) nickel benzene tetracarboxylate,bis(imidazole) nickel oxalate, tetrakis (imidazole) nickel malonate,hexakis (imidazole) nickel hexafluorotitanate, hexakis (imidazole)cobaltous hexafluorotitanate, tetrakis (imidazole) cuprichexafluorotitanate, hexakis (imidazole) nickel phosphate, hexakis(imidazole) nickel monohydrogen phosphate, hexakis (imidazole) nickeldihydrogen phosphate, 2-phenyl-4-methyl-5-hydroxymethyl imidazole,2-phenyl-4,5-dihydroxymethyl imidazole,1-cyanoethyl-2-phenyl-4,5-di(cyanoethylmethyl)imidazole,1-cyanoethyl-2-undecylimidazole trimellitate, 1-cyanoethyl-2-phenylimidazole trimellitate,2,4-diamino-6-[2'-methylimidazolyl(1')]ethyl-s-triazine,imidazole/oxalic acid adduct, 1-cyanoethylimidazole/malonic acid adduct,2-phenylimidazole-isocyanuric acid adduct, silver imidazolatesilver-2-ethyl-4-methyl imidazolate copper(I)-2-phenylimidazolate, andnickel imidazolate. Particularly preferred imidazoles includehexakis(imidazole) nickel phthalate, hexakis(imidazole) nickelpersulfate, 1-cyanoethyl-2-undecylimidazole trimellitate, and1-cyanoethyl-2-phenylimidazole trimellitate.

The metal imidazole salts, i.e., phthalates, carboxylates, oxalates,malonates, titantes, etc., can be prepared by adding a solution of 0.2equivalents of the sodium or potassium salt of the corresponding acid in100 ml water to a solution of 0.1 mol (Ni(OAc)₂ ·4H₂ O and 0.6 molimidazole in 250 ml water at 50° C. After cooling to 5° C., the desiredmetal imidazole salt precipitates, is filtered, washed, and dried.

The composition preferably contains a toughening agent to aid inproviding the desired overlap shear and impact strength. Suitabletoughening agents include polymeric compounds having both a rubberyphase and a thermoplastic phase or being capable of forming, with theepoxide group-containing material both a rubbery phase and athermoplastic phase on curing and which inhibit cracking of the curedepoxy composition.

A preferred class of polymeric toughening agents which are capable offorming, with the epoxide group-containing material, both a rubberyphase and a thermoplastic phase on curing are carboxyl-terminatedbutadiene acrylonitrile compounds having the general formula ##STR25##where R⁴ is hydrogen or a methyl group, r is about 0.90 to 0.6, s isabout 1 to 3, and t is about 16 to 50. The carboxyl-terminated butadieneacrylonitrile compounds are preferably prereacted with a diglycidylether of bisphenol A at, for example, a ratio of 30 to 70 parts byweight of the carboxyl-terminated butadiene acrylonitrile compound to 70to 30 parts by weight of the diglycidyl ether of bisphenol A to increasethe pot-life of the composition and provide increased shear strength athigh humidity. Commercially available carboxyl-terminated butadieneacrylonitrile compounds include Hycar 1300×8, Hycar 1300×13, and Hycar1300×17 available from B. F. Goodrich.

Other preferred polymeric toughening agents are graft polymers whichhave both a rubbery phase and a thermoplastic phase, such as thosedisclosed in U.S. Pat. No. 3,496,250 which is incorporated herein byreference. These graft polymers have a rubbery backbone with athermoplastic polymer grafted thereto. Examples of such graft polymersinclude methacrylate/butadiene-sytrene,acrylate-methacrylate/butadiene-styrene andacrylonitrile/butadiene-styrene polymers. The rubbery backbonepreferably can be prepared so as to constitute from about 95 percent toabout 40 percent by weight of the total graft polymer, and thethermoplastic monomer or group of monomers which are polymerized in thepresence of the rubbery backbone constitute from about 5 percent toabout 60 percent by weight of the graft polymer.

Further preferred polymeric toughening agents which have both a rubberyphase and a thermoplastic phase are acrylic core-shell polymers whereinthe core is an acrylic polymer having a glass transition temperaturebelow about 0° C., such as polybutyl acrylate or polyisooctyl acrylate,and the shell is an acrylic polymer having a glass transitiontemperature above about 25° C., such as polymethylmethacrylate.Commercially available core-shell polymers include Acryloid™ KM 323,Acryloid™ KM 330, and Paraloid™ BTA 731, all available from Rohm andHaas Co.

For the greatest toughening effect, both the carboxyl-terminatedbutadiene acrylonitrile and the core-shell polymers are used incombination in the composition.

The toughening agents are preferably present in the composition in anamount of about 8 to 34 weight percent, more preferably 14 to 28 weightpercent, most preferably 18 to 24 weight percent based on the weight ofthe epoxide resin and polyol in the composition. When a combination ofcarboxyl-terminated butadiene acrylonitrile and core-shell polymers areused, the weight ratio is preferably 3:1 to 1:3, more preferably 2:1 to1:2, most preferably 1:1, respectfully.

The composition preferably contains a flow control agent or thickener,to provide the desired rheological characteristics to the composition.Suitable flow control agents include fumed silicas, such as treatedfumed silica, Cab-O-Sil™ TS 720, and untreated fumed silica Cab-O-Sil™M5, available from Cabot Corp., and short fibers, such as cotton andKevlar™ pulp, a high-temperature polyamide fiber available from DuPontCo., with treated fumed silica being preferred. When the composition isto be used as a structural adhesive, the flow control agent ispreferably present in an amount, e.g. generally about 2 to 5 weightpercent, to provide an observable sag of less than 2 mm, more preferably0 mm.

The composition may contain a reactive diluent to aid in controlling thepress-flow characteristics of the composition. Suitable diluents arecompounds having at least one glycidyl ether terminal portion and,preferably, a saturated or unsaturated cyclic backbone. Examples of suchdiluents include: diglycidyl ether of cyclohexane dimethanol, diglycidylether of resorcinol, p-tert-butyl phenyl glycidyl ether, cresyl glycidylether, diglycidyl ether of neopentyl glycol, triglycidyl ether oftrimethylolethane, triglycidyl ether of trimethylolpropane, triglycidylp-amino phenol, N,N'-diglycidylaniline, N,N,N',N',-tetraglycidylmeta-xylylene diamine, and vegetable oil polyglycidyl ether. The minimumamount of reactive diluent needed to provide acceptable press-flowvalues should be used in the composition as the addition of reactivediluent may reduce the lap shear strength and impact strength. When thecomposition is to be used as an adhesive, the reactive diluentpreferably provides a press-flow value of less than 100 sec., morepreferably less than about 50 sec. when tested according to GM Test9021, Method M using a pressure of 551.6 kPa.

The epoxy resin composition can also contain conventional additives suchas fillers, e.g., aluminum powder, carbon black, glass bubbles, talc,clay, calcium carbonate, barium sulfate, titanium dioxide, silicas,silicates, and mica, with aluminum powder being preferred.

The compositions of the invention preferably have a pot life, i.e.,length of time in which viscosity doubles, of at least 3 days, morepreferably at least 30 days, most preferably more than 60 days at 22° C.and at least 12 hours, more preferably about 3 days, most preferably atleast 14 days at 35° C. Both the selection of the polyol and theimidazole affect the pot life of the composition. Generally, pot lifeincreases when the polyol and imidazole are insoluble in the liquidportion of the composition at temperatures of about 25° to 35° C.

The reactivity of the composition is preferably such that the length oftime for the exotherm to peak when tested using a differential scanningcalorimeter held at a temperature of 137° C. is less than 10 minutes,more preferably, less than 5 minutes, most preferably less than 2minutes.

The epoxy resin compositions, when used as adhesives with electrocoatedgalvanized steel, are capable of providing initial room temperature (22°C.) impact strength of at least 11400 J/m², and impact strengths at -30°C. of at least 2200 J/m² preferably at least 4400 J/m², more preferablyat least 11,400 J/m² and an overlap shear strength of at least 7 MPa,preferably at least 10.5 MPa, more preferably at least 13.5 MPa, whencured at a temperature of 165° C. for 30 minutes. The compositions, inthe preferred embodiments, are capable of retaining impact strength ofat least 2200 J/m², more preferably 4400 J/m², most preferably 11,400J/m² after immersion in boiling water for 24 hours, and are capable ofretaining overlap shear strength of at least 5 MPa, preferably at least7 MPa, most preferably at least 10 MPa, after 24 hours submersion inboiling water and after 10 minutes at 80° C.

To determine lap shear strength and impact strength, samples areprepared using electrocoated galvanized steel coupons (0.8 mm thick,25.4 mm wide, 76.2 mm long) or etched aluminum test pieces (1.6 mmthick, 25.4 mm wide, 76.2 mm long). Each steel coupon is wiped with oil(type KA-45M, available from H. A. Montgomery Co.) using a saturatedcheese cloth. After 10 minutes, excess oil is removed by wiping twicewith a clean cheese cloth. Aluminum coupons are prepared by using an FPL(Forest Products Laboratories) etch (immersion in a sulfuricacid/chromic acid bath) followed by a water rinse and drying. Adhesiveis applied over an end portion of one coupon. Two 2.5 cm lengths of 0.25mm piano wire are placed across the adhesive about 8 mm apart. An endportion (1.25 cm) of a second test panel is placed over the adhesive toform a 1.25 cm overlap. The test panels are clamped at each edge of theoverlap using 0.94 cm capacity binder clips No. 10020 available from IDLMfg. and Sales Corp., Carlstadt, NJ, until the adhesive is cured eitherin a forced air oven at 165° C. for 30 minutes or where the coupons aresteel, by electromagnetic inductive heating using a Lepel TypeT-2.5-1-KC-B-W Model T-254-62 generator, available from Lepel Corp.,with a 4-turn box coil (6.25 cm sq×3.125 cm deep) of 0.47 cm diametercopper tubing for a period of from 2.5 to 3.5 seconds. During inductiveheating, induced current dissipated by the metal as heat heats thesurface of the specimen in contact with the adhesive, thereby initiatingrapid cure.

Lap shear strength is determined using ASTM Test Method D 1002-2initially (after cooling), after immersion in boiling water for 24 hoursfollowed by air drying for 12 hours and at 80° C. by equilibrating thecoupons for 10 minutes at 80° C. in a constant temperature chamber andtesting the coupons while in the constant temperature chamber. Impactstrength is determined on adhered coupons stored at -30° C. for at leasttwo hours and tested immediately after removal from storage, or onadhered coupons at room temperature (about 22° C.) and after immersionin boiling water for 24 hours followed by air drying for 12 hours. Theadhered coupons are supported horizontally about 8 mm from each end andsubjected to impact by a 1680 g steel wedge, 6.35 cm in height andhaving a rounded (6.35 mm radius) nose hardened to Rockwell C-50 to C-60suspended from a fulcrum by a 1.1 cm diameter, 47.6 cm long rod, the rodbeing permitted to swing down from the horizontal to the verticalthrough 90°, and the nose of the wedge impacting the sample as thevertical position is reached.

Sag resistance of the composition is measured on electrocoated steelpanels which have been wiped with oil as for the shear and impactstrength tests. A 0.48 cm diameter bead 10 cm long is applied with acaulking gun on a steel panel lying horizontally. The panel is thenplaced in a vertical position with the bead horizontal. The amount ofsag or slump exhibited by the bead is measured after 4 hours. The beadpreferably sags less than 2 mm. More preferably, the bead exhibits nosag.

The pot life of the adhesive composition is the length of time duringwhich the viscosity of the composition doubles at a given temperature.The reactivity of the composition is the time to cure (exotherm peak)when a 10 mg sample is held at 137° C. in a differential scanningcalorimeter.

In the following non-limiting examples, all parts are by weight unlessotherwise specified.

EXAMPLES 1 AND 2

Adhesive compositions were prepared using the following formulations:

    ______________________________________                                                            Ex. 1 Ex. 2                                                                   (Parts)                                                                             (Parts)                                             ______________________________________                                        DER ™ 332          38.0    44.7                                            Paraloid ™ BTA-731 5.6     6.6                                             Hexakis (imidazole) nickel                                                                          2.9     3.4                                             phthalate                                                                     Trimethylolethane     9.1     10.7                                            Hycar ™ 1300 × 8/DER ™ 332.sup.1                                                        15.9    18.6                                            Cab-O-Sil ™ TS 720 3.5     3.5                                             Aluminum powder       --      12.5                                            Calcium carbonate CS-11                                                                             25.0    --                                              ______________________________________                                         .sup.1 An adduct prepared by blending 60 parts by weight DER ™ 322 wit     40 parts by weight Hycar ™ 1300 × 8, heating the mixture to          80-85° C., adding 0.1 part triphenylphosphine, and reacting the        mixture at 80-85° C. for 2 hours with stirring.                   

In preparing the compositions of Examples 1 and 2, the epoxide (DER™332) is preheated to 120° C., the Paraloid™ BTA 731 is added, and themixture is agitated under high shear for 1 hour at 120° C. A preblend ofthe Hycar 1300×8 adduct, the trimethylolethane and the hexakis(imidazole) nickel phthalate is passed through a paint mill three timesto achieve a uniform mix. These preblends are combined and theCab-O-Sil™ TS720, aluminum powder, and calcium carbonate are added withmixing until a uniform composition is attained.

Samples were prepared as described above using electrocoated galvanizedsteel and cured by inductive heating for the time set forth in Table 1.Tests were run for initial lap shear strength at 22° C., the resultsbeing reported in Table 1.

                  TABLE 1                                                         ______________________________________                                        Cure time     Lap shear strength (MPa)                                        (sec)         Ex. 1      Ex. 2                                                ______________________________________                                        2.7           5.3        5.5                                                  2.8           10.9       8.3                                                  2.9           10.6       9.7                                                  3.0           10.1       11.0                                                 3.1           9.7        11.7                                                 3.2           6.7        11.7                                                 ______________________________________                                    

EXAMPLES 3 AND 4

In Examples 3 and 4, samples were prepared as in Examples 1 and 2,respectively, except that the adhesive composition was cured in a forcedair oven for 30 minutes at 165° C. The samples were tested for initiallap shear strength at room temperature, and after 24 hour immersion inboiling water and for initial lap shear strength at room temperature andafter 24 hour immersion in boiling water. Each composition was testedfor press-flow value. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                   Lap shear      Impact strength                                     Press-flow strength (MPa) (J/m.sup.2 × 10.sup.2) at 22° C.       Ex.  value (sec)                                                                             Initial 24 hour boil                                                                           InitiaI                                                                             24 hour boil                            ______________________________________                                        3    85        14.9    9.8      ≧114                                                                           55                                    4    50        15.0    10.8     ≧114                                                                         ≧114                             ______________________________________                                    

EXAMPLES 5-9

In Examples 5-9, adhesive compositions were prepared as in Examples 1and 2 using the following formulations:

    ______________________________________                                                   Ex. 5 Ex. 6   Ex. 7   Ex. 8 Ex. 9                                             (parts)                                                                             (parts) (parts) (parts)                                                                             (parts)                                ______________________________________                                        Epon ™ 828                                                                              --      48.8    45.8  37.2  36.2                                 DER ™ 332 36.1    --      --    --    --                                   Paraloid ™ BTA-731                                                                      8.5     11.6    10.9  --    18.7                                 Hexakis(imidazole)                                                            nickel phthalate                                                                           2.7     3.6     3.4   2.8   2.7                                  Trimethylolethane                                                                          8.6     11.6    10.9  8.9   8.7                                  Hycar ™ 1300 × 8/                                                                 15.1    20.4    --    22.2  15.1                                 DER ™ 332                                                                  Cab-O-Sil ™ TS-720                                                                      4.0     --      4.0   4.0   3.5                                  Aluminum powder                                                                            25.0    --      25.0  25.0  25.0                                 ______________________________________                                    

Samples were prepared and tested as described above in Examples 3 and 4.The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                   Lap shear      Impact strength                                     Press-flow strength (MPa) (J/m.sup.2 × 10.sup.2) at 22° C.       Ex.  value (sec)                                                                             Initial 24 hour boil                                                                           Initial                                                                             24 hour boil                            ______________________________________                                        5    190       13.7    12.3     ≧114                                                                         102                                     6    103       14.6    10.5     98    100                                     7    551       13.8    12.9     ≧114                                                                          98                                     8     70       13.6    7.9      ≧114                                                                          75                                     9    163       14.5    12.7     ≧114                                                                         114                                     ______________________________________                                    

EXAMPLES 10-34 AND COMPARATIVE EXAMPLE 1

In Examples 10-34, compositions were prepared, using the followingformulation with various polyol curing agents in the amounts shown inTable 4.

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        DER ™ 332           67.2                                                   Paraloid ™ BTA 731  16.0                                                   DER ™ 332/Hycar ™ 1300 × 8 adduct                                                        28.0                                                   Hexakis (imidazole) nickel phthalate                                                                 5.0                                                    Cab-O-Sil ™ TS 720  5.2                                                    Aluminum powder        32.6                                                   Polyol                 --                                                     ______________________________________                                    

The Paraloid™ BTA 731 (toughening agent) is predispersed in the epoxide(DER™ 332) in a high shear mixer at 150° C. and mixed for one to twohours. To this dispersion are added the prepared adduct and thetrimethylol propane. This mixture is mixed for 5 minutes and thencooled. The imidazole catalyst is then added, followed by addition ofthe Cab-O-Sil™ TS-720 and the aluminum powder. Mixing is continued usinga paint mill until all materials are well-dispersed.

In Comparative Example 1, an epoxy resin composition was prepared as inExamples 10-34, except that no polyol was added.

The compositions were tested for pot life and reactivity. Samples wereprepared using electrocoated galvanized stell coupons as describedhereinabove, with oven curing at 165° C. for 30 minutes. Samples testedfor lap shear strength at 80° C. were post-cured at 200° C. for 30minutes. The results are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                          Pot Life         Lap shear      Impact strength                          Amount                                                                             (days)    Reactivity                                                                           strength (MPa) at -30° C.       Ex.  Polyol      (parts)                                                                            22° C.                                                                      35° C.                                                                      (minutes)                                                                            Initial                                                                           24 hr. boil                                                                          80° C.                                                                     (J/m.sup.2 ×                                                            10.sup.2)               __________________________________________________________________________    10   Trimethylol ethane                                                                        14.0  120 18   1.6    4.8 9.4        ≧114             11   Trimethylol propane                                                                       15.6  24  5    1.9    14.7                                                                              11.9   9.2 ≧114             12   Trimethylol amino                                                                         10.6 >60  40   1.7    12.5                                                                              9.4    11.0                                                                              ≧114                  methane                                                                  13   Ethylene glycol                                                                           10.9   8  2    1.4    12.1                                                                              1.0    2.2 ≧114             14   2-butyne-1,4-diol                                                                         15.5   5  1    0.7    13.7                                                                              11.4   3.5 105                     15   Pentaerythritol                                                                           11.9 >60  21   4.1    14.1                                                                              9.5    11.6                                                                              ≧114             16   Dipentaerythritol                                                                         14.9 >60  12   6.7    12.5                                                                              6.1    10.6                                                                              ≧114                  ether                                                                    17   Tripentaerythritol                                                                        10.4 >60  12   9      11.4                                                                              5.3    10.3                                                                              105                     18   1,3-butane diol                                                                           15.7  16  5    2.1    12.5                                                                              1.4    1.8 25                      19   1,4-butane diol                                                                           15.7  15  2    1.2    13.3                                                                              0.7    1.4 31                      20   2-diethyl-1,3                                                                             23.1 >60  7    2.5    11.1                                                                              4.8    2.9 32                           pentane diol                                                             21   2,2'-oxydiethanol                                                                         18.6   7  2    1.2    11.0                                                                              0.7    1.2 36                      22   Glycerol    10.7 >20  5    1.7    9.7 2.8    1.4 31                      23   1,2,4-butane triol                                                                        12.5 >20  3    1.6    13.7                                                                              8.3    8.3 ≧114             24   1,2,6-hexane triol                                                                        17.8 >20  5    1.4    13.8                                                                              9.5    4.1 53                      25   Triethanolamine                                                                           17.0   1  1    1.0    14.7                                                                              6.0    1.7 ≧114             26   1,6-Hexane diol                                                                           20.7  20  3    2.7    13.5                                                                              4.8    1.9 31                      27   2,3-Butane diol                                                                           15.7   7  2    2.6    12.2                                                                              3.5    3.0 34                      28   2-Butene-1,4-diol                                                                         15.6   5  1    0.9    12.7                                                                              2.8    1.4 31                      29   2,2'-Bis(hydroxy-                                                                         14.6 >60  >30  1.7    13.0                                                                              10.2   11.9                                                                              105                          methyl)-2,2',2"-                                                              nitrilotriethanol                                                        30   Tricine     20.9  50  13   6.4    10.5                                                                              0      5.2 38                      31   1,5-Pentane diol                                                                          18.2  10  3    1.5    13.1                                                                              1.0    1.9 32                      32   Dantocol ™ DHE                                                                         37.8  18  3    2.4    14.6                                                                              0.7    1.7 26                           (available from                                                               Glyco, Inc.)                                                             33   2,5-Dimethyl-2,5-                                                                         50.0 >30  >20  2.4    7.2 0      1.7 28                           hexanediol                                                               34   1,4-Cyclohexane-                                                                          25.2 >30  16   3.9    11.0                                                                              6.2    2.3 76                           dimethanol                                                               Comp 1                                                                             none        --   >60  >60  >>10   0.5 7.5    9.6 ≧ 114            __________________________________________________________________________                                                          1                   

EXAMPLES 35-54

In Examples 35-54, compositions were prepared, as described in Examples10-34, using the following formulation with various imidazole catalystsas set forth in Table 5.

    ______________________________________                                                             Parts by weight                                          ______________________________________                                        DER ™ 332           67.2                                                   Paraloid ™ BTA 731  16.0                                                   DER ™ 332/Hycar ™ 1300 × 8                                                               28.0                                                   Trimethylol propane    15.6                                                   Cab-O-Sil ™ TS 720  5.2                                                    Aluminum powder        32.6                                                   Imidazole (various)    5.0                                                    ______________________________________                                    

Electrocoated galvanized steel coupons were prepared and tested for lapshear strength and impact strength. Test results are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                    Pot Life       Lap shear     Impact Strength                                  (days)   Reactivity                                                                          strength (MPa)                                                                              at -30° C.                Ex.                                                                              Imidazole    22° C.                                                                      35° C.                                                                     (minutes)                                                                           Initial                                                                           24 hr. boil                                                                         80° C.                                                                     (J/m.sup.2                       __________________________________________________________________________                                                 × 10.sup.2)                35 1-Cyanoethyl-2-imdecyl-                                                                     15  4   3.2   16.9                                                                              11.8  11.8                                                                              ≧114                         imidazole trimellitic                                                         acid adduct                                                                36 1-Cyanoethyl-2-phenyl                                                                      >60  13  3.1   14.8                                                                              9.0   12.1                                                                              ≧114                         imidazole trimellitic                                                         acid adduct                                                                37 2-Phenyl-4,5-dihydroxy-                                                                    >60  30  4.0   15.3                                                                              9.9   12.4                                                                              84                                  methyl imidazole                                                           38 2,4-Diamino-6-[2'-methyl                                                                    30  5   0.8   15.1                                                                              10.5  3.4 74                                  imidazolyl-(1')]ethyl-s                                                       triazine                                                                   39 1-Cyanoethyl-2-phenyl-4,5-                                                                   2  1   0.6   15.2                                                                              13.3  4.5 51                                  di(cyanoethylmethyl)                                                          imidazole                                                                  40 Imidazole      3  1   0.6   12.6                                                                              12.9  1.4 32                               41 2-Phenyl-4-methyl-5-                                                                        25  4   1.4   14.0                                                                              13.6  8.3 32                                  hydroxymethyl imidazole                                                    42 2-Phenylimidazole/                                                                           3  1   0.8   12.3                                                                              10.5  3.3 27                                  isocyanuric acid adduct                                                    43 Hexakis(imidazole)nickel                                                                    24  6   1.7   14.8                                                                              10.7  11.5                                                                              ≧114                         phthalate                                                                  44 Bis(imidazole)nickel                                                                       >60  16  10.0  15.6                                                                              14.6  10.8                                                                              105                                 oxalate                                                                    45 Hexakis(imidazole)nickel                                                                   >50  12  2.7   13.1                                                                              8.3   8.6 105                                 persulfate                                                                 46 Hexakis(imidazole)nickel                                                                   >50  4   1.3   13.8                                                                              9.9   7.3 42                                  succinate                                                                  47 Hexakis(imidazole)nickel                                                                    40  6   1.5   14.7                                                                              2.4   2.1 32                                  carbonate                                                                  48 Hexakis(imidazole)cobalt                                                                    60  13  2.8   13.5                                                                              1.4   3.7 38                                  hexafluorotitanate                                                         49 Silver-2-methylimidazolate                                                                 >60  30  2.1   15.1                                                                              5.2   12.1                                                                              ≧114                      50 Nickel imidazolate                                                                         >40  7   1.8   16.0                                                                              2.1   10.0                                                                              105                              51 Copper-2-ethyl-4-methyl                                                                     15  10  3.6   15.2                                                                              7.2   6.1 81                                  imidazolate                                                                52 Copper (I) imidazolate                                                                     >60  24  9.0   12.1                                                                              7.9   4.8 32                               53 Copper (II) imidazolate                                                                     30  5   1.9   15.2                                                                              9.0   5.3 31                               54 Silver imidazolate                                                                         >60  13  2.4   12.4                                                                              10.1  3.2 28                               __________________________________________________________________________

EXAMPLES 55-60

Adhesive formulations were prepared as in Example 3, except that thepolyol and amount thereof and imidazole (5 parts in each formulation)set forth in Table 6 were substituted for the trimethylolethane and thehexakis(imidazole)nickel phthalate, respectively.

                  TABLE 6                                                         ______________________________________                                                             Parts                                                    Ex.  Polyol          polyol  Imidazole                                        ______________________________________                                        55   Trimethylol propane                                                                           15.6    Hexakis(imidazole)nickel                                                      phthalate                                        56   Trimethylol propane                                                                           15.6    Hexakis(imidazole)nickel                                                      persulfate                                       57   Trimethylol propane                                                                           15.6    Imidazole                                        58   Trimethylol propane                                                                           15.6    2-Phenyl-4,5-dihydroxy-                                                       methyl imidazole                                 59   Pentaerythritol 11.9    Hexakis(imidazole)nickel                                                      phthalate                                        60   Trimethylol ethane                                                                            14.0    Hexakis(imidazole)nickel                                                      phthalate                                        ______________________________________                                    

Etched aluminum panels were coated using the method describedhereinabove. The panels were cured for 30 minutes at 150° C. and testedfor initial lap shear strength, lap shear strength after immersion inboiling water for 24 hours and impact strength. The results are setforth in Table 7.

                  TABLE 7                                                         ______________________________________                                                              Impact strength                                         Lap shear strength (MPa)                                                                            at 30°                                           Example                                                                              Initial    24 hour boil                                                                              (J/m.sup.2 × 10.sup.2)                    ______________________________________                                        55     24.8       20.8        ≧114                                     56     20.0       16.8        ≧114                                     57     23.4       16.8        93                                              58     24.2       18.4        93                                              59     19.0       17.6        47                                              60     21.0       17.6        93                                              ______________________________________                                    

EXAMPLES 61-72

In Examples 61-72, compositions were prepared as described in Examples 5except that reactive diluents, as set forth in Table 8, were added tothe Paraloid™ BTA 731 and Epon™ 828 predispersion with the formulationsbeing as follows:

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        Epon ™ 828          34.7                                                   Paraloid ™ BTA 731  6.2                                                    Reactive diluent       5.2                                                    Hycar ™ 1300 × 8/DER ™ 332 adduct                                                        14.5                                                   Trimethylolethane      8.3                                                    Hexakis(imidazole)nickel phthalate                                                                   2.6                                                    Cab-O-Sil ™ TS 720  3.5                                                    Aluminum powder        25.0                                                   ______________________________________                                    

Each composition was tested for press-flow value, lap shear strength,and impact strength after curing at 165° C. for 30 minutes. The resultsare set forth in Table 8.

                                      TABLE 8                                     __________________________________________________________________________                       Press                                                                              Lap shear    Impact strength                                             flow strength (MPa)                                                                             at 22° C. (J/m.sup.2 ×                                           10.sup.2)                                                   value    24 hour       24 hour                                                                             Sag                           Ex.                                                                              Diluent         (sec.)                                                                             Initial                                                                           boil 80° C.                                                                     Initial                                                                            boil  (mm)                          __________________________________________________________________________    61 Diglycidyl ether of cyclo-                                                                    60   16.4                                                                              12.4 11.2                                                                              ≧114                                                                        ≧114                                                                         10                               hexane dimethanol (MK-107,                                                    Wilmington Chemical Co.)                                                   62 Diglycidyl ether of                                                                           83   16.4                                                                              10.3 12.1                                                                              ≧114                                                                        ≧114                                                                         8                                resorcinol (WC-69,                                                            Wilmington Chemical Co.)                                                   63 P-tert-butylphenyl glycidyl                                                                   47   14.6                                                                              11.1 8.2 ≧114                                                                        ≧114                                                                         8                                ether (WC-65,                                                                 Wilmington Chemical Co.)                                                   64 Vegetable oil polygly-                                                                        45   14.6                                                                              5.7  --  ≧114                                                                        73.2  7                                cidyl ether (WC-85,                                                           Wilmington Chemical Co.)                                                   65 Cresyl glycidyl ether                                                                         47   15.7                                                                              12.6 6.0 ≧114                                                                        ≧114                                                                         9                                (Epotuf ™ -37053,                                                          Reichold Chemical Co.)                                                     66 Diglycidyl ether of neo-                                                                      36   15.5                                                                              3.6  --  ≧114                                                                        22.8  12                               pentyl glycol Epotuf ™                                                     37054, Reichold Chemical Co.)                                              67 Triglycidyl ether of tri-                                                                     56   15.7                                                                              1.4  --  ≧11                                                                         38.1  13                               methylol ethane (Epi-Rez                                                      5044, Celanese Corp.)                                                      68 Triglycidyl ether of tri-                                                                     62   15.6                                                                              5.8  --  ≧114                                                                        28.9  13                               methylol propane (Epi-                                                        Rez ™ 5048, Celanese Corp.)                                             69 Triglycidyl p-amino phenol                                                                    80   16.2                                                                              12.4 12.8                                                                              ≧114                                                                        ≧114                                                                         7                                (ERL-0510, Ciba-Geigy Corp.)                                               70 Polyglycidylether (DER-736,                                                                   58   16.3                                                                              3.8  --  ≧114                                                                        52.9  9                                Dow Chemical Co.)                                                          71 N,N'-diglycidyl aniline                                                                       92   15.4                                                                              12.0 --  ≧114                                                                        104.6 9                                (Lekuthern ™ x 50,                                                         Mobay Chemical Co.)                                                        72 N,N,N',N'-tetraglycidyl                                                                       148  16.2                                                                              13.4 --  ≧114                                                                        ≧114                                                                         9                                meta-xylene diamine                                                           (PGA-X, Sherwin-Williams                                                      Co.)                                                                       __________________________________________________________________________

EXAMPLES 73-77

In Examples 73-77 compositions were prepared as in Examples 61-63 and 65respectively, except that the amount of Cab-O-Sil™ TS 720 was increasedto 4 parts by weight and in Example 77 a composition was prepared as inExample 61, except the aluminum powder was reduced to 12.5 parts byweight and the Cab-O-Sil TS-720 was reduced to 3.5 parts by weight. Eachcomposition was tested for press-flow value, sag, lap shear strength,and impact strength. The results are shown in Table 9. As can be seenfrom the data in Table 9, an increase in the amount of the flow controlagent or a reduction in the amount of the aluminum powder filer providesimproved sag resistance over that of Examples 61-63 and 65.

                                      TABLE 9                                     __________________________________________________________________________               Press                                                                             Lap shear                                                                              Impact strength                                                  flow                                                                              strength (MPa)                                                                         (J/m.sup.2 × 10.sup.2)                                     value   24 hour    24 hour                                                                             Sag                                       Ex.                                                                              Diluent (sec.)                                                                            Initial                                                                           boil Initial                                                                             boil  (mm)                                      __________________________________________________________________________    73 MK-107  65  15.6                                                                              7.1  ≧114                                                                           65  0                                         74 WC-69   90  14.6                                                                              11.2 ≧114                                                                         ≧114                                                                         0                                         75 WC-65   80  14.3                                                                              9.7  ≧114                                                                         ≧114                                                                         0                                         76 Epotuf-37053                                                                          70  14.8                                                                              10.8 ≧114                                                                         ≧114                                                                         0                                         77 MK-107  46  16.2                                                                              1.8   110    53  3                                         __________________________________________________________________________

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scope ofthis invention.

We claim:
 1. A method for adhering a first substrate to a secondsubstrate comprising the steps of coating said first substrate with astorage-stable, thermally-curable, one part epoxy resin compositioncomprising a curable glycidyl ether epoxide resin; a curative amount ofan aliphatic or non-aromatic cyclic polyol having about 2 to 18 carbonatoms, at least two hydroxy groups of said polyol being primary orsecondary, and said polyol being free of strong acid groups, and free ofelectron-withdrawing substituents and large groups which cause sterichindrance in the α-position in relation to the carbon atoms attached tothe methylol groups of the polyol; said epoxide resin and said polyolbeing present in amounts such that the hydroxyl to epoxide ratio isabout 0.5:1 to 1:1 and a catalytic amount of an imidazole compoundselected from(a) compounds represented by the formula

    M.sup.1 (L.sup.1).sub.a (X.sup.1).sub.b

where M¹ is Ni⁺⁺, Cu⁺⁺, or Co⁺⁺,L¹ is ##STR26## where R² is alkyl having1 to 18 carbon atoms, cyanoalkyl having 1 to 4 carbon atoms, phenyl, orsubstituted phenyl, and R³ is alkylene having 1 to 18 carbon atoms,phenyl, or substituted phenyl, X¹ is --R⁴ (COO⁻)₂ where R⁴ is phenyl,naphthyl, or C_(m) H_(2m-1), where m is 0, 1, or 2, or X¹ is --R⁵(COO⁻)_(e), where R5 is phenyl or naphthyl and e is 3, 4, or 5, or X¹ isan anion of a strong inorganic acid, a is 2, 4 or 6, and b is 0.5, 0.67,1, or 2 depending on the valence of X¹ ; (b) compounds represented bythe formula

    L.sup.2 X.sup.2

whereL² is ##STR27## where R⁶ is --H, --C_(n) H_(2n+1) or ##STR28## nbeing a number of from 1 to 16, R₇ is --H, --CH₃, --C₂ H₅, --C₂ H₄ CN,or ##STR29## R⁸ is --H, --CH₃, --C₂ H₅, --CH₂ OH, or ##STR30## R⁹ is --Hor --CH₂ OH X² is --R⁴ (COOH)₂ where R⁴ is phenyl, naphthyl, or C_(m)H_(2m-1) where m is 0, 1, or 2, or X² is --R⁵ (COOH)_(e) whereR⁵ isphenyl or naphthyl and e is 3,4, or 5, or X² is isocyanuric acid; (c)compounds represented by the formula

    M.sup.3 (L.sup.3).sub.e

whereM³ is Ni⁺⁺, Cu⁺⁺, Co⁺⁺, Zn⁺⁺, Cu⁺, or Ag⁺, L³ ##STR31## where R¹ is--H, ##STR32## or C_(n) H_(2n+1), n being a number of from 1 to 16, andeach R² is --CH₃ ##STR33## or --CH₂ OH, e is 1 or 2; (d) compoundsrepresented by the formula

    L.sup.4 ##STR34##  where R.sup.6, R.sup.7, R.sup.8 and R.sup.9 are the same as for compound (b); and (e) a compound represented by the formula ##STR35##  wherein X, Y and Z may be the same or different, and each may be hydrogen, a lower alkyl or aryl having 1-12 carbon atoms, halo or nitro and said imidazole being insoluble in said epoxide resin at temperatures of about 25° to 35° C.; and said resin composition having a pot life of at least 3 days at 22° C. and at least 12 hours at 35° C., contacting said second substrate with said coated first substrate, and heating said substrates to a temperature in the range of 100° to 200° C. to cure said composition and bond said substrates together.


2. The method of claim 1 wherein said substrates are electrocoatedgalvanized steel.
 3. The method of claim 1 wherein said heating is byelectromagnetic induction.
 4. The method of claim 1 wherein said bondedsubstrates have an initial impact strength of at least about 2200 J/m².5. The method of claim 2 wherein said bonded substrates have an initiallap shear strength of at least about 7 MPa when said heating is at 165°C. for 30 minutes.
 6. The method of claim 2 wherein said bondedsubstrates have a lap shear strength of at least about 5 MPa afterimmersion in boiling water for 24 hours.
 7. The method of claim 2wherein said bonded substrates have a lap shear strength of at leastabout 5 MPa when heated to 80° C.
 8. The method of claim 1 wherein saidimidazole comprises about 1 to 10 weight percent of the composition. 9.The method of claim 1 further comprising at least one toughening agent.10. The method of claim 9 wherein said toughening agent comprises about8 to 34 weight percent of the composition.
 11. The method of claim 1further comprising a flow control agent.
 12. The method of claim 11wherein said composition has a maximum sag of less than about 2 mm. 13.The method of claim 1 further comprising a reactive diluent.
 14. Themethod of claim 13 wherein said composition has a press-flow value ofless than about 100 sec.
 15. The method of claim 1 further comprisingfiller.
 16. The method of claim 15 wherein said filler is aluminumpowder.
 17. The method of claim 1 wherein said composition has areactivity of less than 10 minutes at 137° C.
 18. The method of claim 1wherein said polyol is trimethylol ethane.
 19. The method of claim 1wherein said epoxide is the diglycidyl ether of bisphenol A.
 20. Thecomposition of claim 1 wherein said imidazole is nickel imidazolephthalate.
 21. The method of claim 10 comprising a carboxyl-terminatedbutadiene acrylonitrile toughening agent and a core-shell polymertoughening agent.